No copy - return wasm memory view

README.md

@@ -19,8 +19,8 @@ import { snappyUncompress } from 'hysnappy'
 const compressed = new Uint8Array([
   0x0a, 0x24, 0x68, 0x79, 0x70, 0x65, 0x72, 0x70, 0x61, 0x72, 0x61, 0x6d
 ])
-const output = new Uint8Array(10)
-snappyUncompress(compressed, output)
+const outputLength = 10
+const output = snappyUncompress(compressed, outputLength)
 ```
 
 ## Development

benchmark.js

@@ -14,12 +14,10 @@ const compressed = time(`generate and compress ${fileSize.toLocaleString()}`, ()
 })
 console.log(`compressed ${fileSize.toLocaleString()} bytes to ${compressed.length.toLocaleString()} bytes`)
 
-const output = new Uint8Array(fileSize)
-
 const snappyUncompress = snappyUncompressor()
-timeWithStdDev('uncompress wasm', () => snappyUncompress(compressed, output))
+timeWithStdDev('uncompress wasm', () => snappyUncompress(compressed, fileSize))
 
-// time('uncompress snappyjs', () => uncompress(compressed, output))
+// time('uncompress snappyjs', () => uncompress(compressed, fileSize))
 
 /**
  * @param {string} name

hysnappy.d.ts

@@ -4,9 +4,9 @@
  * @param {Uint8Array} input
  * @param {Uint8Array} output
  */
-export async function snappyUncompress(input: Uint8Array, output: Uint8Array): Promise<void>
+export async function snappyUncompress(input: Uint8Array, outputLength: number): Uint8Array
 
 /**
  * Load wasm and return uncompressor function.
  */
-export function snappyUncompressor(): (input: Uint8Array, output: Uint8Array) => void
+export function snappyUncompressor(): (input: Uint8Array, output: number) => Uint8Array

hysnappy.js

@@ -2,22 +2,23 @@
  * Uncompress a snappy compressed buffer.
  *
  * @param {Uint8Array} input
- * @param {Uint8Array} output
+ * @param {number} outputLength
+ * @returns {Uint8Array}
  */
-export function snappyUncompress(input, output) {
-  snappyUncompressor()(input, output)
+export function snappyUncompress(input, outputLength) {
+  return snappyUncompressor()(input, outputLength)
 }
 
 /**
  * Load wasm and return uncompressor function.
  *
- * @returns {(input: Uint8Array, output: Uint8Array) => void}
+ * @returns {(input: Uint8Array, outputLength: number) => Uint8Array}
  */
 export function snappyUncompressor() {
   // Instantiate wasm module
   const wasm = instantiateWasm()
 
-  return (input, output) => {
+  return (input, outputLength) => {
     /** @type {any} */
     const { memory, uncompress } = wasm.exports
 
@@ -28,7 +29,7 @@ export function snappyUncompressor() {
     const outputStart = inputStart + input.byteLength
 
     // WebAssembly memory
-    const totalSize = inputStart + input.byteLength + output.byteLength
+    const totalSize = inputStart + input.byteLength + outputLength
     if (memory.buffer.byteLength < totalSize) {
       // Calculate the number of pages needed, rounding up
       const pageSize = 64 * 1024 // 64KiB per page
@@ -52,11 +53,7 @@ export function snappyUncompressor() {
     if (result) throw new Error(`failed to uncompress data ${result}`)
 
     // Get uncompressed data from WASM memory
-    const uncompressed = byteArray.slice(outputStart, outputStart + output.byteLength)
-
-    // Copy the uncompressed data to the output buffer
-    // TODO: Return WASM memory buffer instead of copying?
-    output.set(uncompressed)
+    return byteArray.slice(outputStart, outputStart + outputLength)
   }
 }
 

test/decompress.test.js

@@ -40,8 +40,7 @@ describe('snappy uncompress', () => {
 
   testCases.map(({ compressed, expected }, i) => {
     it(`decompress test input ${i}`, () => {
-      const output = new Uint8Array(expected.length)
-      snappyUncompress(compressed, output)
+      const output = snappyUncompress(compressed, expected.length)
       if (typeof expected === 'string') {
         const outputStr = new TextDecoder().decode(output)
         expect(outputStr).toBe(expected)
@@ -52,16 +51,15 @@ describe('snappy uncompress', () => {
   })
 
   it('throws for invalid input', () => {
-    const output = new Uint8Array(10)
-    expect(() => snappyUncompress(new Uint8Array([]), output))
+    expect(() => snappyUncompress(new Uint8Array([]), 10))
       .toThrow('invalid snappy length header')
-    expect(() => snappyUncompress(new Uint8Array([0xff]), output))
+    expect(() => snappyUncompress(new Uint8Array([0xff]), 10))
       .toThrow('invalid snappy length header')
-    expect(() => snappyUncompress(new Uint8Array([0x03, 0x61]), output))
+    expect(() => snappyUncompress(new Uint8Array([0x03, 0x61]), 10))
       .toThrow('missing eof marker')
-    expect(() => snappyUncompress(new Uint8Array([0x03, 0xf1]), output))
+    expect(() => snappyUncompress(new Uint8Array([0x03, 0xf1]), 10))
       .toThrow('missing eof marker')
-    expect(() => snappyUncompress(new Uint8Array([0x02, 0x00, 0x68]), output))
+    expect(() => snappyUncompress(new Uint8Array([0x02, 0x00, 0x68]), 10))
       .toThrow('premature end of input')
   })
 })